When you read a book, you read your own brain. Somehow the chemicals inside your skull turn electrical signals into conscious experience. Colour is one of the most powerful examples: the difference between the red of cinnabar, the yellow of orpiment and the blue of hemimorphite is ultimately a difference in the firing-rate and strength of nerve-signals. But that’s true of the differences between sight and smell, smell and hearing, hearing and touch, and so on. The nerve-signals are essentially the same: it’s the encoding that changes, but the encoding is quantitative, not qualitative. So how do quanta turn into qualia?

This book brings these questions home very strongly, because its images are so powerful. Minerals can be beautiful or ugly, crystalline or formless, dazzling or dull. Yet all those differences, so sharp in the mind, arise from differing arrangements of the same set of subatomic particles. Smooth blue turquoise has the chemical formula CuAl6(PO4)4(OH)8•4H2O; the orange-red crystals of vanadinite have the formula Pb5(VO4)3Cl. Those very different formulas involve different elements, so it’s not surprising that turquoise and vandanite have very different appearances and chemical behaviour.

But all elements are built of three things: protons, neutrons and electrons. On every page of this book you’re just seeing variations on a threme – a theme of three. But “just” isn’t right for the vastness of what’s going on. The differences between minerals are numerical: the three particles are arranged differently and come in different quantities. Of course, there are sub-atomic forces involved too and smaller units at work in the three particles, but the fundaments of matter are far simpler than the shapes, colours and textures that can be produced by mixing those fundaments in varying proportions.

As you’ll see here: variety is the spice of this book. The geologist Ronald Louis Bonewitz discusses basic chemistry, crystallography and collecting techniques, then works his way systematically through the many families of mineral: native elements, sulphides, molybdates, arsenates, and so on, plus organics like coral and amber. Then there’s a shorter section on rocks: igneous, metamorphic and sedimentary, plus meteorites. Each distinct mineral and rock has an individual page with a colour photograph, a formula, a key of its identification features, and a short text discussing its name, chemistry and uses:

Scorodite FeAsO4•2H2O3

A hydrated iron arsenate mineral, scorodite takes its name from the Greek word scorodion, which means “garlic-like” – an allusion to the odour emitted by the arsenic when specimens are heated. Scorodite can vary considerably in colour depending on the light under which it is seen: pale leek green, greyish green, liver brown, pale blue, violet, yellow, pale greyish, or colourless. It may be blue-green in daylight but bluish purple to greyish blue in incandescent light; in transmitted light it may appear colourless to pale shades of green or brown. Crystals are usually dipyramidal, appearing octohedral, and may have a number of modifying faces. They may also be tabular or short prisms. Drusy coatings are common. Scorodite may also be porous and earthy or massive. Scorodite is found in hydrothermal veins, hot spring deposits, and oxidized zones of arsenic-rich ore bodies. Associated minerals may be pharmacosiderite, vivianite (p. 157), adamite (p. 160), and various iron oxides. (“Minerals: Arsenates”, pg. 165)

There’s a lot here to delight the eye, stimulate the mind and twist the tongue, but chemistry always makes me think of consciousness. It’s a fundamental science and it’s been spectacularly successful in both explaining and altering the material world. This book is a triumph of chemistry both as an object and as an exposition.

But chemistry isn’t all-conquering: it’s helpless to explain the mental aspect of the world. My brain is made of the same basic particles as both this book I’m reading and the minerals it’s describing and depicting. But I’m conscious and they’re not. Science has absolutely no idea how to cross the chasm between matter and mind.

This book wasn’t intended to raise that question, but it does for me. And the better it succeeds in its obvious purpose – portraying, describing and explaining matter – the more strongly it knocks on that stubbornly closed metaphysical door.